Definition
Image alt text (alternative text) is the text description associated with an image in HTML email using the alt attribute on the <img> tag. When an email client blocks images from loading — which occurs in approximately 43% of email opens — the alt text is displayed in place of the image. Alt text also serves screen readers, which announce the description to visually impaired users, making it a critical accessibility feature.
The purpose of alt text differs for decorative and informative images. For decorative images such as background patterns, spacers, or purely visual elements, alt="" (empty alt text) is appropriate because it tells screen readers to skip the image entirely. For informative images such as product photos, infographics, or logo images, descriptive alt text conveys the image's content or function. Alt text should describe what the image communicates, not what it looks like.
Gmail renders alt text differently from other clients. When images are blocked in Gmail web, the alt text appears in a coloured placeholder that shows the image dimensions and text. This creates an SEO-like effect where alt text helps recipients understand the email's content even with images disabled. Gmail's image placeholder displays the first few words of alt text, which makes the beginning of the alt text particularly important. Yahoo Mail and Outlook show alt text as a tooltip on hover.
Best Practices
Write descriptive alt text for every informative image. Describe the image's message or function, such as "Woman wearing our autumn collection coat" rather than "Photo of model." Keep descriptions concise and relevant to the email's context.
Use empty alt text (alt="") for purely decorative images. Spacer images, divider lines, and decorative background elements do not need alt text. Empty alt text prevents screen readers from announcing the image unnecessarily.
Front-load the important information in your alt text. Gmail's image placeholder truncates alt text after a few words, so the most critical description should appear first.
Include calls to action in alt text for image-based CTAs. If your primary button is an image, the alt text should say the button text, such as "Shop the sale" or "Download the guide."
Match alt text to the surrounding context. Alt text should make sense in the flow of the email's content, as screen readers may read alt text alongside surrounding text.
Related Glossary Terms
Email Above Fold
The portion of an email visible without scrolling, varying significantly by device, client, and preview pane configuration.
Email Emoji
The use of emoji in email subject lines and body content, with platform-specific rendering differences and measurable engagement impacts.
Email Footer
An email footer is the bottom section of an email that contains legal requirements, unsubscribe mechanisms, and company information.
Email Graceful Degradation
An email design strategy that starts with a feature-rich layout and systematically reduces complexity for clients with limited rendering capabilities.
Email Preview Pane
A UI panel in email clients that shows message content alongside the inbox list, affecting how much of an email is visible before scrolling.
Email Progressive Enhancement
An email design strategy that builds a functional base layout for all clients then layers enhanced features for more capable rendering engines.
Frequently Asked Questions
When images load successfully, alt text is typically not displayed visually. Some email clients show alt text briefly while the image downloads, then replace it with the image. Screen readers may still announce the alt text even when images are visible.
Yes. Gmail web displays alt text inside a coloured placeholder box that matches the image dimensions. This placeholder is highly visible and functions similarly to a text-based image preview. Gmail mobile may not show alt text placeholders as prominently.
Alt text should be concise — typically 10–15 words or 125 characters maximum. Some email clients truncate longer alt text in image placeholders. If a longer description is necessary, consider including it as visible text elsewhere in the email.
Indirectly, yes. Emails with missing or poor alt text can appear suspicious to spam filters, especially if the email has a high image-to-text ratio. Well-written alt text contributes to a healthy text-to-image balance that filters prefer.
No. Each image should have alt text that is specific to that image's purpose. Duplicate alt text on multiple images creates a repetitive experience for screen reader users and provides no additional value when images are blocked.